The invention concerns thermoplastic molding compositions and more particularly compositions that are reinforced with wollastonitemold.
A thermoplastic molding composition having improved impact strength at low temperatures is disclosed. The composition contains A) polycarbonate and/or polyester carbonate B) a graft polymer based on ethylene-xcex1-olefin rubber as graft base, C) wollastonite having carbon content greater than 0.1% relative to the weight of the wollastonite and D) at least one of triglyceride, aliphatic saturated hydrocarbon and aliphatic unsaturated hydrocarbon.
It is known that blends containing AES rubbers and AES resins are weather resistant, but their mechanical properties in the low temperature range are unsatisfactory. At temperatures below 0xc2x0 C. they become brittle and display unsatisfactory impact strengths and this hinders the use of these molding compositions at lower temperatures. In particular, the notch impact strength of AES blends in the low temperature range is poor, especially in comparison to acrylonitrile/butadiene/styrene (ABS) blends.
JP-A 50 109 247 describes polycarbonate blends with AES containing 0.1 to 10 wt. % paraffin oil. JP-A 58 098 354 describes polycarbonate blends with AES and 0.5 to 20 wt. % plasticisers for vinyl polymers. It is not known that the use of special additives, which concentrate specifically in the flexible phase of the blend, leads to a pronounced improvement in low-temperature properties in polycarbonate/AES blends. The compositions thus described display an inadequate rigidity level at room temperature.
Mineral-filled polycarbonate/AES molding compositions are likewise known.
EP-B 0 391 413 describes PC/AES compositions with a low linear and thermal expansion quotient and high impact strength and heat resistance, which contain 4 to 18 wt. % of an inorganic filler, the particles of which have an average diameter/thickness ratio of 4 to 24. They are therefore platelet-like minerals such as talc or mica.
PC/AES molding compositions with fibrous mineral fillers are also known.
PC/AES compositions with wollastonites having an average fibre length of 5 to 25 xcexcm and an average particle diameter of 0.1 to 10 xcexcm are claimed in U.S. Pat. No. 5,965,655. The molding compositions are characterized in particular by improved surface characteristics (xe2x80x9cclass A surfacexe2x80x9d) and a low coefficient of thermal expansion. The wollastonites that are preferably used display an average aspect ratio (i.e. a ratio of fibre length to fibre diameter) of up to 6. Molding compositions with such wollastonites generally have an inadequate rigidity, i.e. too low a tensile/flexural modulus. Furthermore, these molding compositions display brittle fracture characteristics at room temperature.
Compositions consisting of 65 to 85 parts by weight of aromatic polycarbonate, 10 to 50 parts by weight of rubber-modified graft copolymer and 1 to 15 parts by weight of a mineral filler having a maximum characteristic expansion of 0.1 to 30 xcexcm are claimed in WO 98/51737. Talc and wollastonite are disclosed as such fillers. Such PC-rich molding compositions display an inadequate low-temperature impact strength.
EP-A 1 038 920 describes molding compositions containing a special melt polycarbonate, AES and 15 parts by weight of a wollastonite having a particle diameter of 4 xcexcm and an aspect ratio L/D=20. Such molding compositions display an inadequate low-temperature impact strength.
The unpublished German patent application 10 152 317.3 describes impact-modified polycarbonate compositions reinforced with wollastonite of a particular specification. Additives according to component D) of the present invention are not mentioned.
The unpublished patent application 100 542 743.3 describes polycarbonate/AES blends that do contain additives according to component D) of the present invention, but wollastonites of a particular specification are not mentioned.
The object of the present invention was to provide a weather resistant, impact-modified polycarbonate blend that displays notch impact resistant characteristics, a high modulus of elasticity and a low coefficient of thermal expansion, even at low temperatures, and which is therefore very suitable for exterior car body applications in particular.